I'll chip in with some thoughts as well, as some differ from ed's.

Jared Knight - Good prospect, but probably not a high-end scorer. He'll be an NHL player in some capacity though, almost guaranteed.
Rocco Grimaldi - Tons of talent, really small, long ways from an NHL career. He'll more than likely play all 4 years at UND, then a couple in the AHL. Worth holding onto though if you have a large enough farm.
Zach Hamill - Nothing to see here. Definite trade bait but he won't get you much.
Zemgus Girgensons - Very solid, 2nd or 3rd liner in the future. He definitely has value in your multi-cat league, though.
Mathieu Perreault - Another little guy, but he definitely has the talent to put up points. He's shot 14.8, 17.1, and 26.7 percent in his 3 seasons (2 partial). Obviously those are pretty high, especially the 26, but it shows the kind of scoring ability he has.

John Moore - Good prospect, but there are SO many young defenders in Columbus....he might get lost in the shuffle. Good trade chip though.
Jamie Oleksiak - He's showing more offense than I expected, and could develop into a very good player especially in a multi-cat. Keeper.

Leland Irving - I still believe in his chances....Brust and Taylor are only competition at the AHL level, Irving is still the best bet for an NHL future. Kipper is getting older, Karlsson is not starter material, and Ramo is only a maybe although he'd probably jump ahead of Irving if he came back to the NHL. He's worth holding onto unless you can add him into a nice deal.
Mikko Koskinen - Not much to see here imo. He's firmly 3rd on the prospect chart behind Poulin and Nilsson. Not worth an outright drop unless you really need the space, but I wouldn't expect much from him, either.

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20 Team Dynasty (points per) - G (25, 50 for defense) A (25) PIM (3) +/- (5) PPG (15) SHG (25) OTG (15) GWG (25) HTr (50) GP (2) HIT (1) BLK (1) Use actual NHL salary

F: Malkin, Tavares, E. Kane, Parenteau, Havlat, Tarasenko, Galchenyuk, Brunner, Boyes, Kruger, Helm, M. Martin, Bergenheim, Carcillo, Stajan

D: Green, Ehrhoff, Ekman-Larsson, Coburn, Daley, Postma

G: Fleury, Mason, Montoya

Farm: Grigorenko, Grimaldi, Kucherov, D. Shore, Hartikainen, Stransky, Kerdiles, Joensuu, Pageau, Murphy, Ceci, Klefbom, Thrower, Donovan, Ekholm, Lehner, Dansk, Poulin, Nilsson, Andersen